Electric rotary furnace



A 2, 1932- B. M. s. KALLiNG ET AL 1,870,053

ELECTRIC ROTARY FURNACE Filed Dec. '7, 1929 Patented Aug. 2, 1932 UNITED STATES PATENT OFFICE MICHAEL STUBE KALLING AN D CARL VON DEL'W'IG, OF AVESTA, SWEDEN, ASSIGNOBS TO A. JOHNSON CO 0F STOCKHOLH, SWEDEN, A COMPANY OF SWEDEN ELECTRIC ROTARY FURNACE Application filed December 7, 1929, Serial No. 412,518, and in Sweden December 10, 1828.

The present invention has for its object the provision of devices in rotary furnaces, 1ntended for reduction of iron ore with carbon without smelting or for other similar pur- 5' poses, whereby the heat necessary for the process is generated in the charge by means of electric current which is passed through the same.

The use of a suitable construction of elec- 0 trodes is of essential importance. for the op eration of rotary furnaces intended for carrying out the present method. If, as hitherto 0 may sinter or cake on the wall at some point between the electrodes. Thereby the electrical resistance is at this point resulting in a concentration of the current causing a further rise of the temperature and an increased caking of the iron. In such a way a bridge of iron rapidly may be formed between the electrodes so that a short circuit and interruption in the work arise. According to the present invention the electrodes are arranged either in such a way that the electrodes do not come into contact at all with the walls of the furnace chamber or so that the electrodes come into contact with the walls of the furnace, either the lining or masonry, only along a short part of the periphery of the furnace,

so that said contact line will be comparatively short in relation to the effective surface of the furnace. According to the present invention electrodes in form of radially arranged rodlike members may be used which for each phase advantageously may be placed as the spokes in a wheel. The contact line between the electrodes and the wall of the furnace may then be made very short and still form a stable construction. For the said purpose the electrodes may, however, also be arranged in any other way than that shown on the drawing. Thus. the electrodes may also be formed as rings or circular discs having a smaller diameter than the furnace chamber and kept in position at the furnace wall only by means of one or more supports which simultaneously may serve for conducting the current to the electrodes thus formed.

A good result may be attained also by other constructions based on the same idea. Of greatest importance is that the contact lines between the electrodes and the wall be eliminated or be made as short as possible particularly in the hottest zone of the furnace. In the cooler parts of the furnace such a contact, can cause no inconvenience. Thus the electrodes may be advantageously carried by supporting members fastened to the wall of the furnace at some distance from the current conducting zone.

Another advantage gained by constructing the electrodes in such a way that the main part of the effective surface thereof will be placed at some distance from the furnace wall is that the essential part of the generation of heat takes place at a certain distance from the furnace wall so that said wall may be kept cooler and thus the losses of heat due to radiation be reduced.

The electrodes may be made of carbon, graphite, iron, some heat resisting alloy or othler suitable electricallyconducting mater1a s. a

The furnace may be used for single-phase current as well as for poly-phase current. Particularly simple and suitable for the purpose in question is an arrangement of elec trodes for two-phase current according to Scotts coupling. In this case three systems of electrodes are placed one after the other in the longitudinal direction, the outside elec trodes for each a phase and the middle one for the common return phase.

In the reduction process in question it is also important 'for the economical accomplishment of the process that the high carbon monoxide gas formed in the zone for the final reduction be utilized as far as possible in the process as either the reducing agent or the source of heat. This is possible to a higher degree only if the ore is prereduced by the gas before the ore and the carbon have been mixed. A higher content of carbon dioxide may then be obtained in the escaping gas than is carbon simultaneously were present. I

According to the present invention said result is attained by providing that the furnace at the feeding end with a central tube suitably of some heat resisting alloy, sai tube reaching some distance into the furnace. The ore is fed through said tube, preferably in form of concentrate or finely divided ore, and the gas passes out in opposite direction thereby effecting prereduction of the ore. The carbon material is fed into the furnace outside the tube through some suitable lock device in order to revent the gas from escaping this way. n order to obtain a satisfactory prereduction of concentrate or finely divided ore, it should first be heated which simply may be done by burning the remainin combustible gas in the outer endof the tu e (i. e. the feeding end of the furnace) by supplying air from outside through a tube of smaller diameter. Hereby roasting of the ore and purifying it from sulphur may also be attained. If the carbon material is moist and if it is not desired to allow all this moisture to enter into the furnace chamber that part of the tube in which the ore is prehehted may suitably be surrounded by a drum into which the carbon is charged before being sy lied to the furnace. The heat trans m1 fed through the wall of the central tube then heats and drys the carbon material.

For illustrating the invention there is shown oh the accompanying drawing as exampletwo forms of construction of the electrodes adapted to be used in a rotary furnace which is constructed according to an invention made by the applicants being object for an application for patent filed simultaneously with this application.

Figure 1 shows the furnace in longitudinal section.

Figure 2 is a cross section on the line C-C .in Figure 1.

Figure 3 shows a section on the line 13-13 in Figure 1.

Figure 4 shows a section on the line A-A in Figure 1.

Figure 5 shows part of the furnace in longitudinal section provided with another form of construction of the electrodes.

1 is the rotary furnace proper which in a known manner is carried by rotatable rollers 2, two and two connected by means of a shaft 3 and possibly formed in such 'a way that they may serve to rotate the furnace. 4 is tube or tube formed combustion cham ber centrally arranged inside the furnace, said tube being carried by supporting members 5 and on one side communicating with the inner parts of the furnace chamber through the opening 6 and on the other side at the feeding end. being provided with an opening serving for feeding the charge into the combustion chamber. According to the form of construction shown the chamber 4 outside the furnace 1 has an enlarged part 8 servin as preheating chamber and surroundedTy a drum 9 connected to the rotary furnace. The gas formed during the reduction passes the tube 45 and the preheating chamber 8, and the combustible parts of the gas are burnt by means of air supplied through the pipe.l0. The carbon (and possibly also another charge material) is fed into the drum 11 through the opening 29, said drum surrounding the preheating chamber 8, where it is preheated and dried, where-. after it passes into the furnace chamber 13 through a lock device 12. The lock device may be made of a suitable number of partitions walls 14., each at the periphery provided with an opening 15 arranged in such a way in relation to each other that during the rotation of the furnace one of said openings is wholly immerged in the material or the carbon fed into the furnace said material thus preventing gas from the interior of the furnace from escaping through the feeding opening for the carbon. A similar'lock device 12 is arranged also at the discharge end of the furnace, provided with a discharge opening 17 so that the treated material may leave the furnace without allowing the gas or any appreciable part thereof from the interior of the furnace to escape the same way. For cooling the treated product the discharge end of the furnace may be provided with a cooling chamber 18 for instance in form of a flangelike enlargement, entering into the container 19 for cooling water.

will be seen from Figure 3 the walls of the chamber 18 can possibly be corrugated so as to provide a greater cooling surface; The cooling chamber 18 may possibly be in the form of a lock device in an analogous manner to that above described making the locl device 12 superfluous.

a The electrode device according to Figures 1 and 2 are constructed as rodlike members 22 extending from a central part 23 in a manner similar to that of the spokes in a wheel. As will be seen from Figure 2 said rods are tapered at their outer ends 24 which are in contact with the masonry or inner wall so that the part of the periphery along which each electrode is in contact with the wall (the contact line) will be very short compared with the whole effective surfaces of the electrodes 25, i. e. the surfaces serving for transmission of current from one electrode to the other through the charge.

Each electrode 25-is provided with a part 26, in a. known manner being in conductive connection with the conductors 28, 28 for supplying electric current.

According to the form of construction of the electrodes shown in Figure 5 the elecof the furnace, and they are carried by supports 27 extending through the parts of the walls of the furnace chamber where the temperature is not as high as in the heating zone, i. e. the zone between the electrodes 25 or adjacent said electrodes.

In this case the above mentioned disadvantage of local overheating and disturbances in the process arising from the formation at the furnace wall of a conducting bridge between the electrodes during the process caused by iron sponge-and other reduced electrically conductive product is reduced or wholly eliminated.

By regulating the outlet for the treated product by a lock device 12 as above described a uniform discharge of the products formed is attained and an accumulation of material between the electrodes deleterious for the uniform operation of the process is prevented, which also contributes to lessen the rise of local overheating between the electrodes in the heating zone.

The line H-H indicates the horizontal plane. The furnace slopes in relation to the horizontal plane in such a way that the axis thereof at the feeding end lies higher than at the discharge end, so that the material automatically will pass through the furnace during the rotation thereof.

Having now described our invention we declare that what we claim is 1. In an electric rotary furnace, electrodes for conducting current through the ore, means for supporting the electrodes inside the furnace with the major part of each electrode out of contact with the furnace wall,

.. said means comprising circular disc electrodes of smaller diameter than the inside diameter of the furnace taken at the maximum-heat zone thereof, and supports for said discs engaging with the furnace walls for positioning said discs out of direct contact with the walls of the furnace.

2. In an electric rotary furnace, electrodes for conducting current through the ore, means for supporting the electrodes inside the furnace with the major part of each electrode out of contact with the furnace wall, said means comprising circular disc electrodes of smaller diameter than theinside diameterofthe furnace takenat the maximum-heat zone thereof, and supports for said discs engaging with the furnace walls for positioning said discs out of direct contact with the walls of the furnace, said supports engaging the furnace walls at points outside the maximum heat zone and having portions extending into said zone and bearing said electrodes thereat.

3'. In an electric rotary furnace, electrodes for conducting current through the material to be treated located in transverse planes of :the surface and spaced from each other in the axial direction of the furnace, and means for supporting the electrodes inside of the furnace substantially out of contact with the inner circumference of the furnace wall.

4. In an electric rotary furnace, electrodes for conducting current through the material to be treated located in transverse planes of the surface and spaced from each other in the axial direction of the furnace, a means for supporting the electrodes inside of the furnace substantially out of contact with the inner circumfer nce of the furnace wall, and means for supplying polyphase alternating current to said electrodes.

In testimony whereof we aifix our signatures.

BO MICHAEL STURE MLLING. CARL VON DELWIG. 

